1. Filed of the Invention
The present invention relates to a modulation circuit utilized in a mobile radio communication transmitter.
2. Description of the Related Art
For voice transmission in a mobile communication system, usually an analog transmission using a frequency modulation is utilized, because of the effective use of a frequency band, high quality transmission, small apparatus and the like.
Although a modulation circuit using phaselocked loop is widely used as mentioned hereinafter, it is necessary that a lock-up time of the phase-locked loop be quick and a maximum frequency deviation of the frequency modulation wave be approximately flat within a transmission band.
Explanations regarding related art will be given later with reference to the attached figures.